Reviewed by Lexie CornerApr 3 2024
Adhesion is how the human body maintains its structural integrity. Tendons connect muscle and bone, whereas muscle and skin are connected by connective tissue.
These biomimetic mechanical characteristics provide the foundation of hydrogel-based soft materials, a new design for biomedical implants, bioinspired soft robots, and human-machine interfaces. Before they can completely replace frequently used hard materials, several obstacles remain to be addressed.
The National Science Foundation (NSF) awarded Qihan Liu, an assistant professor of mechanical and materials science at the University of Pittsburgh Swanson School of Engineering, a $546,127 Faculty Early Career Development Award to investigate thermodynamic interaction as a potential means of overcoming adhesion in soft materials.
Professor Liu is an outstanding researcher, and this CAREER award will bolster activities in at least two core research competencies in our Department of Mechanical Engineering and Materials Science, specifically advanced manufacturing and design and soft matter biomechanics.
Brian Gleeson, Professor, Swanson School of Engineering, University of Pittsburgh
Gellin’ It Together with Thermodynamics
Hard materials are often built using screws and interlocking structures, allowing a machine to be easily improved or maintained by replacing parts. Adhesion in soft materials is now irreversible, making it practically hard to modify or repair a soft machine in the same way that conventional machines can.
Despite the extensive research on gel adhesion, there is a critical unmet need for stimuli-responsive adhesion that not only has a strong grip but also detaches and reattaches and is reversible under designated stimuli like temperature, stress, and the presence of certain chemicals. We are learning that thermodynamic interaction between hydrogels can make this possible.
Qihan Liu, Assistant Professor, Swanson School of Engineering, University of Pittsburgh
Sticky When You Need It
Thermodynamic adhesion differs from previous studies of bonding-based adhesions.
There are two types of thermodynamic adhesion mechanisms: osmocapillary and electrostatic adhesion. Osmocapillary adhesion is caused by the suction created when a nearby hydrogel absorbs the interfacial solvent, which is determined by the thermodynamics of osmosis. Electrostatic adhesion is the attraction of oppositely charged polymer networks surrounded by free ions.
Liu added, “Both types of thermodynamic adhesion respond to a wide variety of stimuli and can be reversible, which is our main goal. We need to build a predictive model that can test thermodynamic adhesion under different conditions to determine if it's a feasible solution.”
Using thermodynamic interaction with hydrogels can lead to a variety of applications. A smartwatch, for example, can be worn without a band and used in conjunction with invasive medical devices.
In addition to the scientific contributions of adhesion in soft materials, Liu's CAREER award will assist him in developing a video style that is both easy for researchers to create and interesting for laypeople to watch, encouraging the direct dissemination of cutting-edge research to the general public via free video-sharing platforms.
The five-year project, titled “Robust, Reversible, and Stimuli-responsive Thermodynamic Adhesion in Hydrogels,” will begin in May 2024.